This invention relates to colored objects of constant appearance and method and, more particularly, to colored objects and method for coloring same to achieve an improved constancy of color appearance upon changes of illumination.
The colors of clothing, furnishings, food-packaging, safety-colors around dangerous machinery, should all retain their desired color whatever illumination is used. Improvement in color-constancy would be helpful indeed in all walks of life--in clothing, make-up, decorator colors, automobiles, etc. But commercial lamplight is quite liable to distort, change, and even hide the desired colors of these objects whose colors are important in many ways to the human observer.
It has not been known how to design the colors of objects so that the perceived colors of the objects are optimally constant, as illumination is changed. Of course the spectral composition of some illumination, such as sodium lamplight, is such that color distortion cannot be avoided.
Some years ago, the Illuminating Engineering Society was actively concerned with color-constancy of safety-colors, which must reliably indicate both dangerous environments and havens, in both natural and poorly-designed commercial illumination. At that time the present applicant found that, rather than depend on the illuminant for color-constancy, one can redesign the spectral reflectances of the safety-colors; they will then more nearly retain their prescribed hue in poor lamplight. What brought about the improvement was to maximize reflectance at specific wavelengths, namely, wavelengths near 450 nm in the blue-violet, 530 nm in the green, and 610 nm in the orange-red, and to minimize reflectance in the blue-green and yellow. The role of these colors is paramount in various visual phenomena in which chromaticity, or perceived color, of an object needs to be controlled. This work is reported in J. Illum. Eng. Soc., Vol. 6, pgs. 92-99 (1977) article entitled "The Design of Safety Colors" by W. A. Thornton. Other pertinent work is reported in U.S. Pat. No. 3,877,797 issued Apr. 15, 1975 to W. A. Thornton, and in Color Research and Application, Vol. 10, pgs. 73-83 (1985) article entitled "Methods for Generating Spectral Reflectance Functions Leading to Color-constant Properties", by R. S. Berns and F. W. Billmeyer, Jr.